Last month it emerged that there had been a 400% rise in police use of “stop and search” powers. And according to a recent Guardian report, there is evidence that black people are being disproportionately targeted. This is profoundly depressing. There are real grounds for concern that, once again, use of this policing strategy is storing up trouble.

Our new report, Beyond Contagion, published today, supports the view that stop and search can have unintended but significant social and psychological consequences. We examined patterns of data in the 2011 riots – in particular how these events arose and spread. The significance of the riots is indisputable: this was the largest wave of disorder in the UK since the 1980s, and involved an estimated 20,000 people, with more than 4,000 arrests. It is important to understand the underlying causes.

In our research, we drew upon a comprehensive dataset including videos, social media, interviews and crime data. One part of our analysis looked at differences between those London boroughs that saw rioting and those that did not. Of the different factors we looked at, deprivation (using the 2010 Index of Multiple Deprivation) was the one that correlated most strongly with whether or not a borough saw rioting. Another part of our analysis examined Metropolitan police survey data. This found that prior negative attitudes to the police, including the belief that the police did not treat people with respect, correlated positively with the number of riots per borough.

We also examined the stop and search figures for London for 2009, 2010 and January-July 2011 (the months prior to the August 2011 riots). We included all categories of stop and search in the analysis, and adjusted the figures for borough population size. We found that the boroughs with more stop and search in the two and a half years beforehand were those more likely to see rioting in August 2011. To illustrate this point, the population-adjusted average number of stop and searches in 2010 in the 26 boroughs that saw rioting was 8,442 per 100,000 population, which was more than double the average number (4,141) for those six boroughs that didn’t see rioting.

One interpretation of this finding is that stop and search was a factor in the riots. A correlation is not a cause, of course, so this data alone can’t demonstrate a connection. However, when we re-analysed some of the extensive interview data collected as part of the Guardian’s Reading the Riots project, there did seem to be a connection.

It was a minority of interviewees who described having experiences of stop and search. But it was a large minority. Twenty of 66 participants involved in the riots at Brixton, Clapham or Croydon referred to stop and search and other forms of police attention they described as unfair.

These encounters with the police had several features that illuminate the social relations generated by stop and search. First, stop and search was a deeply humiliating experience. Second, the humiliation was experienced communally as well as individually. Therefore it didn’t matter whether people had personally experienced stop and search; they saw these and similar encounters with the police as an attack on “us”. Third, people used these experiences to explain both their hostility to the police and their participation in the riots.

When people are already feeling alienated and deprived, police interventions such as stop and search put a face on the antagonistic other. They serve to create an embattled community – a community in which opposition to the police is part of the shared identity around which people mobilise.

We note that last year’s rise in the number of stop and searches was accompanied by a slight fall in the number of arrests. The discrepancy between the number of stop and searches and the number of arrests was also a feature of the period immediately before the riots. In Haringey in 2009, for example, only 4.8% of those stopped and searched were arrested, meaning that more than 30,000 unsuccessful searches were made in the borough that year.

From the police perspective, these figures might suggest that stop and search is not efficient. The College of Policing’s own research report concluded that there is “only limited evidence of stop and search having acted as a deterrent [to crime] at a borough level”. From the perspective of the black and working-class young people who are disproportionately targeted, the discrepancy between searches and arrests only supports the perception that stop and search is a form of collective harassment.

Stop and search is deeply toxic, especially when people feel that they are being stopped because of their class or ethnicity. Our research suggests that it is a critical part of the social process whereby riots occur. Unless we stop seeing stop and search as a solution rather than part of the problem, they will happen again.

• John Drury is a professor of social psychology at the University of Sussex. The Beyond Contagion project was carried out by Drury, Roger Ball, Clifford Stott, Stephen Reicher and Fergus Neville